1. Field of the Invention
This invention relates generally to a video signal reproducing apparatus, and more particularly, to improvements in such apparatus for avoiding skew distortion when reproducing is effected when the magnetic tape or other record medium is stopped.
2. Description of the Prior Art
In a conventional video tape recorder (VTR), two transducers or heads are provided having air gaps with different azimuth angles for recording and reproducing signals in the next adjacent or alternate tracks, respectively, in order to minimize cross-talk while permitting an increase in the recording density. This is relatively easy to do, because an apparatus for magnetically recording and/or reproducing video signals frequently includes a rotary guide drum provided with two alternately operative transducers or heads which are diametrically opposed and which can have air gaps with different azimuth angles. The magnetic tape is wrapped helically about a portion of the perimeter of the guide drum and is moved longitudinally while the transducers or heads are rotated, thus causing the heads alternately to scan respective tracks on the tape for recording or reproducing signals recorded therein. In the recording operation of the foregoing helical scan type VTR (video tape recorder), each head effects magnetization of magnetic domains in the magnetic coating on the tape in what would appear to be, if such domains were visible, a series of parallel lines or stripes each having a length as great as the width of the track, and each having an orientation that corresponds to the azimuth angle of the gap of the respective transducer or head. In the reproducing or playback operation of the apparatus, each track is scanned by the transducer or head having its gap aligned with the parallel, but fictitious, lines of that track, from which it follows that the gap of the transducer or head scanning a track for reproducing the video signals recorded therein extends at an angle to the aforementioned fictitious lines of the tracks next adjacent to the track being scanned. By reason of the foregoing, if a transducer or head, in scanning a track for reproducing the video signals recorded therein, overlaps a next adjacent track or otherwise reproduces signals recorded in a latter, the well-known azimuth loss will result in attenuation of the cross-talk signal reproduced from the next adjacent track.
Further, it is the usual practice to record video signals with so-called H-alignment so as to avoid interference or cross-talk from the horizontal synchronizing and blanking signals included in the video signals recorded in the successive parallel tracks. In recording video signals with H-alignment, the ends of the margins between the successive areas in which line intervals are recorded in each track are aligned, (in the direction transverse to the lengths of the tracks), with the adjacent ends of the margins between the successive areas in which line intervals are recorded in the next adjacent tracks.
If, during reproducing operation of the helical scan type VTR, the speed and direction of movement of the tape are equal to the standard type speed and direction, respectively, for recording, then the scanning path of each rotary head or transducer can be made to accurately coincide with a respective one of the record tracks for properly reproducing the video signals recorded therein, and the above described measures are effective for substantially eliminating cross-talk in respect to signals recorded in the tracks next adjacent the track being scanned.
Generally, in practical embodiments of the helical scan type VTR, the standard tape speed for recording is conveniently selected in relation to the diametrical size of the guide drum so that the video signals are recorded with the H-alignment in the nearest to each other tracks recorded by the same head. However, it is sometimes required that during recording the magnetic tape is moved with different tape speeds other than the standard tape speed for increasing the recording density of the video signal thereon. Then, it is not possible to provide an apparatus in which the video signals are recorded with H-alignment when the tape is advanced at two or more different speeds. For example, if the video signals are recorded with H-alignment when the tape is longitudinally driven or transported at a predetermined speed, the signals will not be recorded with H-alignment when the tape is transported at one-half such predetermined speed.
Now, if the tape speed during reproducing is substantially different from that for recording, or if the direction of tape movement during reproducing is different from that during recording, the scanning path of each head may be at a sufficiently large angle to the direction along the recorded tracks so that, in traversing such scanning path, each head will move along, and reproduce video signals from first one and then another of the nearby tracks which have the positions of the recorded horizontal synchronizing pulses offset, for example, by 1/2 the horizontal period (H). If such signals reproduced from first one track and then another during a single field interval are demodulated and fed to a television receiver, a disturbance or jump of 1/2H occurs in the continuity of the horizontal synchronizing pulses at the change over of the reproducing head or transducer from one track to the other. During the scanning period in which the automatic frequency control (AFC) circuit of the television receiver absorbs the jump of 1/2H, a skew distortion will appear in the reproduced picture.
In order to avoid the skew distortion of the reproduced picture, there has been already proposed a new circuit arrangement by the same applicant in U.S. patent application Ser. No. 078,774 filed Sept. 25, 1979, now U.S. Pat. No. 4,283,737, in which the reproduced video signals are delayed by an amount corresponding to the offset distance between the horizontal synchronizing pulses recorded in nearby tracks, and when operating with such different reproducing speed, a switching circuit alternately provides the video signals as reproduced by the head and the delayed reproduced video signals, respectively, with the state of the switching circuit being changed-over each time the reproducing head, in moving along the scanning path, moves from one to the other of the nearby tracks.
On the other hand, there is another type of VTR, in which there are at least two main rotary heads having different azimuth angles to each other and an auxiliary rotary head having the same azimuth angle as that of one of the main rotary heads and which is disposed to substantially scan the same track as scanned by one of the main rotary heads. For slow motion reproduction of the recorded video signals, the tape is intermittently driven by tracks of one frame at every predetermined time interval corresponding to the slow motion ratio, and when the tape is stopped, the video signals are alternately reproduced by one of the main rotary heads and the auxiliary rotary head, while the video signals are alternately reproduced by the two main rotary heads while the tape is moving.
When the above delay circuit arrangement is applied to the new type of VTR described above, the delay circuit arrangement itself becomes complicated and it becomes difficult to control the delay circuit.